1. Technical Field
The present invention relates to a pneumatic tire, and particularly to a pneumatic tire having a wear indicator on a tread surface.
2. Background Art
Conventionally, a wear indicator indicating the state of progress of wear of a tread sometimes is provided on a tread surface of a pneumatic tire, and various technologies are proposed. For example, JP-A 2001-030721 discloses that a plurality of indicators having a different depth (for example, series of numeric strings) is provided side by side on a tread surface, and the numerals disappear in sequence with the progress of wear, thereby reading a wear amount (that is, residual depth of tread groove).
WO2004/050390 discloses the technology that a multi-stage hole is provided on a tread surface, and the contour shapes of the respective stages of the hole is changed to circle, square, triangle and the like, whereby a wear amount is indicated by the change of the contour shape of the hole with the progress of wear.
JP-A 2006-056508 proposes a wear indicator having a shape visually showing the wear amount and having a different shape in a depth direction as a wear indicator provided on a tread surface, and specifically discloses the constitution that pictorial symbols such as smiley face change to different pictorial symbols with the progress of wear.
However, the technology disclosed in JP-A 2001-030721 is that a cross-sectional shape of the indicator does not change in a depth direction. As a result, to indicate a wear amount, a plurality of indicators must be provided side by side, and this becomes a factor of uneven wear.
On the other hand, WO2004/050390 and JP-A 2006-056508 disclose to change a cross-sectional shape of the indicator with the progress of wear, but the wear amount such as residual depth of a groove is not easily indicated visually. JP-A 2006-056508 contains the description that a piled blade forming piled numerals indicating the level of wear of a tread may be used, but does not specifically disclose that how the piled numerals are formed.